1. Field of the Invention
The present invention generally relates to a technology for performing Internet protocol (IP) multicast communication, and specifically relates to a technology for performing IP multicast communication on systems that operate on session control protocols.
2. Description of the Related Art
Recently, communication systems, such as an Internet telephone system, that uses the session initiation protocol (SIP) that controls multimedia sessions over an IP network, have been developed.
When performing IP multicast communication with a SIP-based communication system, to enhance security, it is desirable that terminals that communicate with each other exchange an encryption key, and communicate by messages that are encrypted with the encryption key.
J. Arkko et al., “RFC 3830, MIKEY: Multimedia Internet KEYing” ([online], August 2004, retrieved from the Internet: <URL: http://www.ietf.org/rfc/rfc3830.txt>) discloses a technology called as Multimedia Internet KEYing (MIKEY), which is a standardized protocol for exchanging an encryption key applicable to SIP. When applying a method according to J. Arkko et al. to SIP, terminals that perform encrypted communication exchange an encryption key in accordance with an offer-answer model in principle.
However, in the method according to J. Arkko et al., the terminals need to exchange the encryption key one to one, so that there is a possibility of increasing a processing load during the IP multicast communication.
For example, when performing the IP multicast communication with an IP multicast group in which a number of terminals are registered as a member, each member of the IP multicast group need to exchange a key with all the other members in the group. Because the IP multicast communication can be started only after the key exchange of all the members has completed, it takes longer time to start the communication thereby resulting in lower cost performance. Furthermore, members of the multicast group are fixed, consequently, therefore, for example, a multicast to a group of terminals that is grouped based on presence information cannot be performed.